1. Field of the Invention
The present invention relates to an ink supply system, a recording apparatus, a recording head, and a liquid supply system, by which, for example, a liquid such as ink is stably supplied with no wasted liquid from ink tanks and the like as a liquid storage section to a recording head, a pen, and the like as a liquid use section, and a gas in a liquid chamber between a liquid use section and a liquid storage section is exhausted into the liquid storage section.
2. Related Background Art
As a liquid use apparatus, there has been, for example, an ink jet recording apparatus, which forms an image on a recording medium, by giving liquid ink to the recording medium with an ink jet recording head. Recently, such a recording apparatus has been used in many cases for recording including color recording, because the recording apparatus can make comparatively small noises at recording and form small dots with a high density. As one form of such an ink jet recording apparatus, some of the apparatuses install an ink jet recording head, which is provided with ink tanks in an integrated or a detachable manner, and to which ink is supplied from the ink tanks, and comprise a carriage with which the recording head scans (main scanning) the recording medium in a predetermined direction, and conveyance means which conveys (sub-scanning) the recording medium in the direction perpendicular to the main scanning direction relatively to the recording head. The ink jet recording apparatus performs recording by discharging ink from the recording head during the main scanning process of the recording head. Furthermore, the ink jet recording apparatus installs a recording head, which can discharge a black ink and colored inks (yellow, cyan, magenta, and the like), on the carriage, to perform not only monochrome recording of a text image with the black ink, but also to permit full-color recording by changing discharging rate of each color. It becomes important in such an ink jet recording apparatus to appropriately exhaust a gas such as air, which is mixed into, or exists in an ink supply path, becomes important.
Here, the gas which goes into an ink supply system can be roughly classified into the following four groups according to causes for generation of the gas:    1) a gas going into the system from ink discharge ports of the recording head, or a gas generated along with ink discharge operation;    2) a gas separated from a gas dissolved in ink;    3) a gas which permeates into the system through a material forming the ink supply path from the outside; and    4) a gas which goes into the system when the ink tanks in a cartridge form are exchanged.
Incidentally, ink flow paths formed in the ink jet recording head have a very fine configuration to require ink supplied from the ink tanks to the recording head to be in a clean state without mixed foreign substances such as dust. That is, when the foreign substances such as dust are mixed, there is caused a problem that, especially, the narrow discharge ports in the ink flow paths of the recording head, or sections of liquid flow paths which are directly communicated with the ports are clogged with the foreign substances. Thereby, normal discharge operation of ink cannot be performed, and recovery of functions of the recording head can not be realized in some cases.
Then, it is general in many cases to have a configuration in which filter members which remove foreign substances in ink are arranged in the ink flow paths between ink supply needles, which are plunged into the ink tanks, in the recording head and the recording head, and the filter members prevent the foreign substances from entering the inside of the recording head.
On the other hand, the number of the ink discharge ports has been recently increased in order to achieve higher recording speed, and the employed frequency of a driving signal applied to an element which generates energy by which the ink is discharged has become higher and higher. Thereby, ink consumption per unit time has been remarkably increased, too. Accordingly, it is natural that the amount of ink passing through the filter members is increased. In order to reduce pressure loss of the ink at the filter members, it is effective to arrange filter members with a large area by expanding parts of the ink supply paths. However, as, in this case, a bubble which enters into the ink supply paths easily remains in space at the upstream side of the filter members in the expanded section on the ink supply paths to cause a state in which the bubble can not be discharged, there is a possibility that smooth supply of ink is blocked. Moreover, there is a possibility that the ink is caused not to be discharged, too, because the gas remaining in the ink supply paths becomes very small bubbles, and the bubbles are mixed into the ink which is guided to the discharge ports of the recording head.
Accordingly, it is strongly required to remove the gas remaining in the ink supply paths, and the following methods will be listed for removing the gas:
(1) Method by which a Gas is Removed by Cleaning Operation
One of methods by which a gas is removed is the following method by cleaning operation.
As the ink jet recording head performs recording by discharging the ink, which is liquid, as a droplet from the discharge ports arranged opposing to the recording medium, increase in the ink viscosity, ink solidification, adhesion of dust to the discharge ports, mixing of bubbles into liquid flow paths inside the discharge ports, and the like occur due to evaporation of an ink solvent from the discharge ports, and the discharge ports are clogged, and the like. Accordingly, there is a possibility that poor recording is caused.
Therefore, the ink jet recording apparatus is provided with capping means which covers the discharge ports of the recording head when recording is not operated, or a wiping member which sweeps, as required, the surface (discharge-port forming surface) of the recording head on which the discharge ports are formed. The capping means has not only a capping function by which drying of ink at the discharge ports is prevented when recording is not operated, as described above, but also a function by which clogging of the discharge ports is eliminated. For example, when clogging of the discharge ports is caused, the discharge port forming surface is covered with a cap member of the capping means, and ink is sucked and discharged from the discharge ports by a negative pressure applied in the cap member with a suction pump and the like which is communicated with the inside of the cap member. Thereby, clogging in the discharge ports, which is caused by ink solidification, and defective discharge of ink due to thickened ink or mixed bubbles in the flow path are eliminated.
Thus, forced discharge processing of ink, which is performed as described above in order to eliminate the defective discharge of ink, is called cleaning operation. The cleaning operation is carried out when recording is restarted after the long-time inactive state of the recording apparatus, or when a switch and the like for cleaning is operated by a user who recognizes that the quality of a recording image is deteriorated. After forced discharge of ink from the discharge ports, and, then, wiping operation is done to wipe the discharge port forming surface with the wiping member made of an elastic plate such as rubber. Moreover, there has been a trial in which the bubbles remaining in the ink flow paths are exhausted by the high flow speed of ink in the ink flow paths under application of the large negative pressure on the discharge-port forming surface under capping by driving the suction pump at a high speed at cleaning operation which is performed at initial filling of ink, at which ink is filled in the recording head for the first time, or at exchanging of the ink tanks.
However, as that the sectional areas of the ink flow paths are also increased when the areas of the filter members are made larger in order to control dynamic pressures at the filter members in the ink supply paths, the high flow speed of ink is not generated at the above-described cleaning operation even under application of the large negative pressure in the ink flow paths. Thereby, it is extremely difficult to remove the remaining bubbles from the discharge ports with the suction pump. That is, as a predetermined flow speed is required for the ink passing through the filters as one condition on which the bubbles can pass through the filters by an ink flow generated by the negative pressure caused with the suction pump, the pressure difference across the filters is required to be large in order to generate the predetermined flow speed. In order to realize the pressure difference, it is usually considered to reduce the filter areas for increase in flow path resistance, or to adopt a suction pump with a large flow rate. However, the ink is wastefully consumed, because the supply performance of the ink to the recording head is deteriorated when the filter areas are reduced, and a large amount of ink is discharged when the gas is removed with the suction pump with a large flow rate.
Accordingly, there are two other methods by which bubbles are removed: a method by which bubbles are directly discharged to the outside; and another method by which bubbles are moved to, and are remaining in regions in which the bubbles do not block ink supply. But, the former method, by which a communication port communicating with the outside is arranged in the ink supply paths, among the above two methods is judged not to be preferable, based on the after-described reasons.
(2) Method by which Bubbles are Directly Exhausted to the Outside
In many ordinary ink jet recording apparatuses, a negative pressure is generated in ink storage space of ink tanks in order to prevent an unfavorable leakage of ink from discharge ports of a recording head by disposing capillary force generation members such as absorbers in the ink tanks, or, by arranging elastic members such as springs in flexible ink storage bags to apply an urging force to the ink storage bags so that the inner volumes of the bags are increased. In such a case, when a mere communication port through which bubbles are directly exhausted to the outside is arranged in an ink supply path, air enters into the space from the communication port and the negative pressure will be released. Accordingly, it is required to dispose a pressure-regulating valve and the like at the communication port, and the structure of an ink supply system, that is, the recording apparatus is made complex, or large. Moreover, in order to prevent a leakage of ink from a discharge port which exhausts bubbles, it is required to dispose a water-repelling film and the like through which a gas can pass, but liquid can not pass, or, to adopt a device (a mechanism for detection of the amount of bubbles, an opening and closing mechanism for the communication port, and the like) by which the communication port is opened to exhaust bubbles only when there are remaining bubbles, and, then, there is a possibility that the manufacturing costs are increased and the structure is made complex and larger.
(3) Method by which Bubbles are Moved to, and are Remaining in Regions (for Example, Ink Tanks) in which the Bubbles do not Block Ink Supply
Then, a method by which bubbles are moved to, and are remaining in regions (for example, ink tanks) in which the bubbles do not block ink supply will be considered. In such a method, the inner volume of the ink tank can be configured to be unchanged, and a generated negative pressure can be assumed to be constant, if it is possible to transfer an amount of ink corresponding to the volume of bubbles moving to an ink tank. The above configuration is preferable, because the negative pressure in equilibrium with a holding force for a meniscus formed at a discharge port can be applied on the recording head. Moreover, a gas can be completely removed from the ink supply system when the ink tank is of a cartridge form, because the ink tank is exchanged for a new one when the remaining amount of the ink for storing runs out of the tank.
Here, it is considered to be effective in order to smoothly transfer the gas to the side of the ink tank that an expanded section is provided in an ink supply path in which a filter member is arranged, as described above; and, furthermore, a portion in the upstream side of the filter member in the expanded section is formed to be, for example, tapered toward the upstream side; that is, the ink supply path running from the ink supply needle in the side of the recording head toward an installing position of the filter member is formed not to rapidly be expanded. However, in many ink jet recording apparatuses which has been widely widespread for household use ink tanks in a cartridge form, which separately store black ink and color ink, are configured to be installed in the recording head or a carriage equipped with the head in such a way that the ink tanks can be installed from the top in a detachable manner. The ink cartridge has, for example, a configuration in which the ink can be supplied to the recording head by plunging a hollow ink supply needle, which is installed upward in the carriage, into the cartridge. Therefore, the pipe diameter of the ink supply needle connecting the ink cartridge and the recording head is an important factor. In other words, a thin ink supply needle is required in order to make installation operation of the cartridge simple, but when the ink supply needle is thin, a force of an ink meniscus formed at a pipe section becomes too large to smoothly move the bubbles.
(4) Proposed Example of a Mechanism by which a Gas is Moved to the Side of an Ink Tank
Some mechanisms by which the gas is moved to the side of the ink tank have been proposed so far.
For example, the Japanese Patent Application Laid-Open No. H05-96744 has disclosed a configuration in which the side of the recording head is separated to a first chamber comprising an air communication port and a second chamber comprising a capillary force generation member, wherein air is supplied to the side of the ink tank through one of the communication paths by connecting the first chamber and the ink tank through two or more communication paths which are different in the heights of openings at the side of the first chamber. In this configuration, the air communication port can be arranged in the first chamber, because a negative pressure is applied to ink in a recording head by the ink head difference between the first chamber and the second chamber, or with the capillary force generation member arranged in the second chamber.
Moreover, the U.S. Pat. No. 6,460,984 has disclosed a configuration in which when it is assumed that a storage chamber for a negative pressure generation member and a liquid storage chamber can be separated, a gas can be securely taken in by arranging a gas priority intake path and a liquid flow-out path in a communication section which connects the intake path and the flow-out path.
Furthermore, the U.S. Pat. No. 6,347,863 has disclosed an ink container (ink container 50) in which a liquid flow-out pipe (drain conduits 66, 72, 74), and a gas intake pipe (vent conduits 76, 82, 84) are protruding downward, wherein an upper opening of the liquid flow-out pipe and an opening of the gas intake pipe are arranged on a bottom surface of an inner wall and inside a storage space for the ink container, respectively.
Moreover, the U.S. Pat. No. 6,022,102 has disclosed a configuration in which a replenisher tank can be connected to a reservoir tank comprising a storage chamber for a negative pressure generation member and an ink storage chamber. And, when the replenisher tanks are connected to the upper portion and the lower one of the space of the ink storage chamber, ink is taken into the ink storage chamber from the replenisher tank through a liquid communication pipe at the lower portion, and air is taken into the side of the replenisher tank from the ink storage chamber through an gas communication pipe at the upper portion.
Furthermore, the U.S. Pat. No. 6,520,630 has disclosed a configuration in which a sub-tank for adding ink to a main tank communicated with a recording head is installed in the upper portion of a main tank, a gas in the main tank is taken into the sub-tank by acceleration and deceleration of a carriage, and ink in the sub-tank is supplied to the inside of the main tank.
However, according to the configuration disclosed in the Japanese Patent Application Laid-Open No. H05-96744, air is taken in the ink tank, depending on the supply of ink, in order to consume the ink in the ink tank which will not change its shape, and the object is not to remove bubbles remaining in an ink supply path. Especially, the negative pressure is not generated in the first chamber which is the ink supply path, and the first chamber is in contact with the atmosphere at any time, because the first chamber is open to the atmosphere through the air communication port. But, the Publication has described no matter unique to a sealed ink supply system at all, that is, in the Publication, there has been no description on the exhaust of the gas which is remaining in the ink supply path of a sealed system formed between the ink tank and the recording head.
Moreover, in the U.S. Pat. No. 6,460,984, there has been described only on a configuration in which the capillary force generation member and the air communication port are arranged between the ink tank and the recording head, and the ink supply path, in the same manner as that of the Japanese Patent Application Laid-Open No. H05-96744, is a system which is open to the atmospheric, and allows free passage of a gas through from the opening as an air communication port. But, the Publication has described no matter unique to a sealed ink supply system at all, that is, in the Publication, there has been no description on the exhaust of the gas which is remaining in the ink supply path of a sealed system formed between the ink tank and the recording head.
Furthermore, the object of technologies disclosed in the U.S. Pat. No. 6,347,863 is to provide a system in which the member (14) comprising the reservoir (reservoir 16, 18, 20) is refilled with ink, but not to remove bubbles remaining in the ink supply path downstream from the reservoir, and in portions using ink. Moreover, it is considered that, as the heights of the openings at the lower portions of the liquid flow-out pipe and the gas intake pipe are equal to each other, liquid and gas cannot be moved when the menisci of ink is formed in the above pipes. In addition, as there are no communication ports realizing communication between the ink storage container and the member (14), and no elements adjusting the negative pressure there is a possibility that, when use of ink is continued, the negative pressure in the inside rapidly rises and ink can not be supplied to portions using the ink.
Moreover, the configuration common to the above patent documents is a configuration in which the liquid storage section (ink tank) which can be separated is in communication with the side of the recording head through a plurality of communication paths, and the air intake unit is provided at a position downstream from the above communication paths (at the side of the recording head). Hereinafter, disadvantages of the configuration according to the U.S. Pat. No. 6,520,630 as a typical example will be described.
FIG. 9 shows a conceptual view of the configuration disclosed in the U.S. Pat. No. 6,520,630. Assuming that the air movement (gas movement to a sub-tank 22 through a pipe 56A) is stopped, the balance among forces applied on the ink meniscus section formed in a pipe 56A will be studied, referring to FIG. 9. In the first place, forces applied downward are a head pressure P1 of ink in the sub-tank 22, and a meniscus force formed at an opening section of the pipe 56A. Moreover, a force applied upward is a pressure P2 by a gas in a main tank 20. The air movement has stopped, because balance among the above forces is realized. In this case, the pressure P2 of the gas in the main tank 20 and a head pressure P3 at the position of the ink liquid level in the main tank 20 are balanced with each other. In addition, as the inside of the sub-tank 22 and that of the main tank 20 are communicated with each other through a pipe 56B, the difference between the downward ink pressure which is applied on the meniscus formed in the pipe 56A and the gas pressure P2 in the main tank 20 is equal to a head pressure difference P4 between the head pressure at the position of the meniscus and that of the liquid level in the main tank 20. Consequently, the head pressure difference P4 and the meniscus pressure are balanced with each other to cause an equilibrium state.
For example, when bubbles are further taken in from the bubble generation device 104 in the above equilibrium state, the liquid level in the main tank 20 gets low, and the head pressure difference P4 between the menisci in the pipe 56A and the liquid level is increased. And, when the head pressure difference P4 exceeds the meniscus pressure, the gas in the main tank 20 is taken into the sub-tank 22 (air movement) through the 56A, and the ink in the sub-tank 22 is supplied to the main tank 20 through the pipe 56B, along with the air movement.
However, as there is caused ink flow in the whole supply system in FIG. 9 when ink is discharged with a recording head 18, pressure loss corresponding to the quantity of the ink flow in the pipe 56B is generated in the sub-tank 22 and the main tank 20. Thereby, the pressure loss is required to be considered for the relation between the above-described meniscus pressure and the head pressure difference P4 (head pressure difference between the meniscus and the liquid level). Consequentially, when the head pressure difference P4 is larger than a pressure which is obtained by adding the pressure loss to the above-described meniscus pressure, air movement will be generated. In other words, in a state in which ink is discharged, gas-liquid exchange (air-ink exchange) is not performed unless comparing with a state in which air movement is stopped, unless the ink liquid surface in the main tank 20 gets low by the pressure loss of the pipe 56B corresponding to the quantity of the ink flow. When the ink liquid level at gas-liquid exchange is lower than the opening section of the pipe 56B, the gas-liquid exchange is not done, and the ink in the main tank 20 is completely used without using the ink in the sub-tank 22.
Accordingly, when the pipes 56A and 56B are made thinner for simple operation by which the tank is installed as described above, the pressure loss corresponding to the quantity of the ink flow is increased, and the ink liquid level in the main tank 20 at gas-liquid exchange gets low. Therefore, the size of the main tank 20 is increased, and, consequently, the size of the whole recording apparatus becomes large.
In addition, there is a possibility, as another issue, that bubbles generated in a bubble generation device 104 are drawn into a flow path in communication with the recording head when ink is discharged for the recording head 18, because the bubble generation device 104 is disposed in the lower portion of the main tank 20. Especially, when the quantity of the ink flow is increased for high speed recording, use-up of ink, and drawing of bubbles into the recording head 18 are easily occurs. Therefore, when the quantity of the ink flow caused by ink discharge of the recording head 18 is restricted, or when the bubble generation device 104 is separated from a filter 39, the size of the main tank 20 is further increased in order to prevent such drawing of the bubbles.
These disadvantages are similarly applied to a configuration in which an air intake unit is provided not in a communication path between a recording head and an ink tank, but in the side of the recording head, that is, to the configuration disclosed in the U.S. Pat. No. 6,022,102. As the U.S. Pat. No. 6,520,630 has the configuration in which the unit (bubble generation device 104) by which air is taken into the main tank 20 is provided while the main tank 20 in communication with the sub-tank 22 comprises a flexible ink bag 100, the above-described disadvantages are similarly applied to the Publication U.S. Pat. No. 6,520,630, like the Publication U.S. Pat. No. 6,022,102.
As described above, the above-described patent literatures have disclosed that a gas is taken into the ink tanks. But, the Publication has described no matter unique to a sealed ink supply system at all, that is, in the Publication, there has been no description on the exhaust of the gas which is remaining in the ink supply path of a sealed system formed between the ink tank and the recording head. Moreover, the publications have included no description on the smooth transfer of the gas in the ink supply path of the sealed system to the side of the ink tank for remaining of the gas therein.